This invention generally relates to motor control in air conditioning systems. More particularly, this invention relates to monitoring the condition of relay contacts for controlling motors in air conditioning systems.
Typical air conditioning systems have compressors and blowers. A variety of strategies for powering the compressors and blowers are in use. One arrangement includes relay switches that are operated to selectively supply power to various portions of the blower motor, for example. In one arrangement, a blower motor includes two windings. One winding is powered to operate the blower at a low speed while a second winding is powered to operate at a high speed.
It has been found that during installation, for example, the relay contacts for controlling the low blower speed have been inadvertently welded together when the relay contacts should be normally opened. Having relay contacts that do not operate properly presents the potential for supplying excessive power to the low speed blower motor winding, for example, which results in a need for repair or replacement. This is one example situation where relay contact operation should be monitored to prolong the longevity of the product and components.
There is a need for a device that monitors the operation of relay contacts and controls associated components to prevent, for example, excessive power being supplied to certain components under certain operating conditions. This invention addresses that need.
This invention is a relay contact monitoring device that is able to detect when at least one relay contact is not operating as intended and responsively controls the operation of selected components to avoid an undesirable result caused by the non-operating relay contacts.
A device designed according to this invention includes a monitoring portion that monitors a voltage across the contacts of a selected relay switch. If an expected voltage is not present, the monitoring portion responsively controls the supply of power to at least one other component to prevent an undesirable amount of power being transmitted across the monitored relay switch.
In one example, the relay monitoring portion includes an opto isolator that operates responsive to the presence of a voltage across the selected relay switch contacts. When the relay switch operates as expected, the opto isolator is de-energized. When the relay switch releases as expected, the opto isolator is energized and provides an output signal for energizing another component, which in turn, controls the operation of a second relay switch. In the event that the first relay switch is not operating as intended, the opto isolator is not energized and the output signal for operating the other component is not provided.
This invention is particularly well suited for controlling the supply of power to a two stage motor having a first winding that is powered at a first level for a low blower operation level and a second winding that is powered at a second, higher power level for a high blower operation. Of course, this invention is not limited to such an arrangement and the various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows.